When you connect to internet and IP is assigned to your computer by your ISP.
At the ISP's end your ip is logged for records and MAC address is stored for security reason.
MAC is short for Media Access Control. The MAC address is the hardware address that uniquely identifies each network device on the Caltech network. The MAC address is also sometimes called the ethernet address.
Many of us believe that by changing their IP they will be treated as new users, but in real time you are identified by your MAC Address.
Your IP is re-assigned each time you connect to internet but what can we do to change MAC address (our real identity).
Since a long time there is a myth between half knowledge people that MAC address can't be changed. But you can change it using a few simple tricks.
Change you Mac address visit
Difference between IP address and MAC address